This invention relates to an image forming apparatus of a kind having a photosensitive sheet transported between a pair of pressure rollers and more particularly to such an apparatus which uses as photosensitive sheet a light receiving sheet coated with microcapsules encapsulating a colorless dye and a radiation curable agent and superposes thereon an image receiving sheet coated with a developing agent to pass them together between the pair of pressure rollers.
A method of forming an image by using such a light receiving sheet as photosensitive sheet has been disclosed, for example, in Japanese Patent Publication Tokkai 58-88739. The light receiving sheet is formed by coating a base sheet with microcapsules which encapsulate a colorless dye and a radiation curable material such as a photopolymerizing monomer such as a selectively hardened image can be formed thereon by exposure to an image carrying beam of light. If an image forming sheet coated with a developing agent is superposed on such a light receiving sheet with a selectively hardened pattern formed thereon and pressed together therewith between a pair of pressure rollers, a visible image can be chromogenically formed on the image receiving sheet.
To explain the above more in detail, a selectively hardened pattern is formed on the light receiving sheet by exposure to an image carrying beam of light reflected from an original document to be copied because only those of the microcapsules exposed to light energy are hardened. When an image receiving sheet is superposed on such a selectively hardened pattern and compressed together, those of the microcapsules which have not been hardened by exposure to light rupture and thereby cause the encapsulated dye to flow out and to chromogenically react with the developing agent on the image receiving sheet.
Pressure rollers which are used for such a purpose must be able to apply a fair large pressure on the sheets which are passed therebetween. The required linear pressure may be about 90 kg/cm. Because such a large pressure must be applied on the sheets that pass between the rollers, however, the sheets tend to wrinkle and/or travel on a zigzag path. This also tends to cause a jam near the pressure rollers.